Compound photoelectric conversion devices having a semiconductor thin film as a light absorbing layer have been developed. In particular, thin-film photoelectric conversion devices having, as a light absorbing layer, a p-type semiconductor layer with a chalcopyrite structure have high conversion efficiency and thus promising applications. Specifically, thin-film photoelectric conversion devices having a light absorbing layer of Cu(In,Ga)Se2 as a Cu—In—Ga—Se compound, Cu(In,Al)Se2 as a Cu—In—Al—Se compound, Cu(Al,Ga)Se2 as a Cu—Al—Ga—Se compound, or CuGaSe2 as a Cu—Ga—Se compound have relatively high conversion efficiency. A thin-film photoelectric conversion device has alight absorbing layer of a p-type semiconductor layer with a chalcopyrite structure, a kesterite structure, or a stannite structure. Such a thin-film photoelectric conversion device generally has a structure including a soda-lime glass substrate, and a molybdenum bottom electrode, a p-type semiconductor layer, an n-type semiconductor layer, an insulating layer, a transparent electrode, a top electrode, and an antireflective film, which are stacked on the substrate. The conversion efficiency η is expressed by η=Voc·Jsc·FF/P·100, wherein Voc is open-circuit voltage, Jsc is short-circuit current density, FF is power factor, and P is incident power density.
This shows that the conversion efficiency increases as the open-circuit voltage, the short-circuit current, and the power factor increase, respectively. Theoretically, as the band gap between the light absorbing layer and the n-type semiconductor layer increases, the open-circuit voltage increases, whereas the short-circuit current density decreases. It is known that the band gap of Cu(In,Ga)Se2 increases with Ga concentration and when Ga/(In+Ga) is controlled about 0.3, the band gap of Cu(In,Ga)Se2 becomes about 1.05 eV. It is known a photoelectric conversion device with high conversion efficiency can be obtained when Ga/(In+Ga) is near to above mentioned value.
Sputtering, vapor deposition, or MOCVD (Metal Organic Chemical Vapor Deposition) is applied for forming the transparent electrode. When a thickness of the transparent electrode is 1 μm or more, interference colors occurs and an optical absorption reduces, these can be reasons for a reduction in the conversion efficiency. Then, processes for reducing optical absorption loss, for example, forming an antireflective film such as NaF on the transparent electrode are applied. However alternative material or method is desired because such processes increase material cost and number of process.